U.S. debt is like a Hallmark movie boyfriend who eventually gets dumped for a small town firefighter, budget watchdog warns 

This rom-com formula is now a staple of holiday TV programming: a busy professional from the big city goes back home for Christmas and falls for a local guy after admitting her current boyfriend wasn’t her true soul mate.

According to Martha Gimbel, executive director of the Yale Budget Lab, this trope could also describe the bond market’s feelings about U.S. debt.

During a Senate hearing this week, she was asked what might trigger a debt crisis and why it hasn’t happened yet despite the explosion of borrowing in recent years. Gimbel replied it’s basic supply and demand, and investors are settling for the easier option, even if it doesn’t meet all their needs—they simply don’t have a better option right now, but that may not always be the case.

“The way that I sort of put it is we are currently the boyfriend at the beginning of the Hallmark movie in the big city where the girlfriend is still going out with him even though she knows that it’s wrong,” she explained. “But at some point she’s gonna go home to the small town and find the nice firefighter and realize that there’s another option.”

For now, as Gimbel explained, investors are settling for the status quo, but it’s only a matter of time before we hit a Sleepless in Stagflation moment and investors find better options. Much like a would-be suitor exaggerating how big their heart is, publicly held debt is pretty substantially—it already is as large as the U.S. GDP, and it will exceed the all-time record set after World War II in the comings years. Publicly held debt then will continue marching higher with no sign of abating as retiring baby boomers drive up entitlement spending.

Like the big-shot professional visiting the small town, treasury bonds are still in high demand, especially for now as a safe-haven asset, despite all the turmoil from President Donald Trump lately. The U.S. debt market remains by far the largest and most liquid, underpinned by the dollar’s status as the world’s reserve currency.

While Gimbel said she doesn’t know when U.S. debt will fall out of favor, the eurozone has been trying to make its debt more appealing to investors.

Europe is a top holder of U.S. debt, so any shift away from Treasuries could worsen the outlook by sending yields higher and adding to borrowing costs.

In 2021, Europe launched the Next Generation EU borrowing program financed through joint debt issuance. While intended as a pandemic-era stimulus program, the breakthrough measure was seen as boosting the euro’s status as reserve asset.

To be sure, other countries also have safe haven assets, including Germany and Scandinavia. But individually, their debt and currency markets aren’t big enough to fill the needs of global finance.

Gimbel pointed out that investors have piled into Switzerland lately, adding that the U.S. is fortunate that Swiss financial markets can’t absorb that much capital.

Helped by low debt levels and a reputation as a secure financial hub, Switzerland has long been seen as a safe haven. That sent the Swiss franc soaring 12.7% against the dollar last year as Trump’s trade war jolted markets. It shot up further this year after Trump threatened to seize Greenland from Denmark.

The war on Iran could worsen the U.S. debt outlook as additional military spending adds to the deficit, while higher bond yields due to oil-fueled inflation translate to bigger interest costs.

“The more we make ourselves less attractive to markets, the more likely it is that you will have a fiscal crisis,” Gimbel warned. “We are literally relying on the fact that markets have no place to go.”

This story was originally featured on Fortune.com